The present invention relates to an adhesive sheet suitable as an adhesive layer for a semiconductor connecting substrate used for mounting a semiconductor integrated circuit, an adhesive-backed tape used for tape automated bonding (TAB) (hereinafter called xe2x80x9ca tape for TABxe2x80x9d), an adhesive-backed tape used for wire bonding connection (hereinafter called xe2x80x9ca tape for WBxe2x80x9d), and a semiconductor connecting substrate and a semiconductor device using any of the foregoing.
Conventional semiconductor integrated circuit (IC) mounting techniques include the following.
For mounting an IC, a method in which the electrodes of the IC are wire-bonded to metallic lead frames and sealed by a resin is most popularly used. IC packages produced in this manner are usually provided in such forms as the small outline package (SOP) and the quad flat package (QFP). In contrast to these, as smaller-sized and lighter-weight electronic apparatuses, a ball grid array (BGA), in which connection terminals are arranged on the surface of a package, are being used (FIG. 1).
The BGA method is characterized in that solder balls (almost as many as the pins of the corresponding IC) are provided in a grid-like form as external connectors of the IC connecting substrate. For connecting an apparatus onto a printing wire board, the apparatus is placed on the board in such a manner that the solder ball faces conform with the conductor pattern of an already printed solder, and the solder is rendered molten by reflow to achieve the desired connection. The most important feature is that although the conventional QFP, etc. allows only the surrounding edges to be used for arranging connection terminals, BGA allows the surface of the connecting substrate to be used, so that more connection terminals can be arranged in a small space. This size reducing effect is more intensified in the chip scale package (CSP), and it may be called a xcexc-BGA (micro BGA) in view of its similarity (FIG. 2).
In the BGA method, for the necessity of keeping the solder ball faces flat for better radiation, a method comprising the steps of laminating a material such as a metallic sheet for reinforcement, radiation, electromagnetic shielding, etc., to the wiring board layer for connecting an IC, using an adhesive sheet, and curing by heating is generally adopted for producing a connecting substrate.
A connecting substrate for BGA is described below with reference to FIG. 4. A connecting substrate for BGA consists of at least one wiring board layer (being constituted by an insulator layer 26 and a conductor pattern 27) for connecting an IC, at least one layer 29 without any conductor pattern formed (functioning as a reinforcing sheet, radiation sheet or shielding sheet, etc.), and at least one adhesive layer 28 for laminating them. In FIG. 4, symbol 25 denotes an organic insulation film; 27, an inner lead; and 30, a solder resist.
For the adhesive layer (adhesive sheet) referred to here, a thermoplastic resin or silicone elastomer (Japanese Patent Publication (Kokoku) No. 6-50448), etc. is proposed for obtaining the effect of easing the thermal stress caused by the difference in thermal expansion coefficient of different materials such as the printed wiring board, solder balls, wiring board layer and the layer without any conductor pattern formed, during temperature cycles and reflow.
On the other hand, as the wiring board layer, a glass epoxy laminated sheet (rigid sheet) had been used, but in recent years, the use of a semiconductor connecting substrate in which a conductor pattern for connecting an IC is formed on an organic insulating film of a polyimide, etc. is increasing. A package using such a tape-like connecting substrate (pattern tape) is generally called a TCP (tape carrier package), and the TCP of a BGA method in particular is called a TAB-BGA or T-BGA.
A TCP has an advantage in that low cost packages can be mass-produced by continuously mounting using a long pattern tape. As for the IC connection method, the tape automated bonding (TAB) method in which bump electrodes of an IC are thermally pressure-bonded to the inner leads of a connecting substrate (by gang bonding or single point bonding) is typical, but a method in which the conductor pads of a connecting substrate and the electrodes of an IC are wire-bonded to each other (hereinafter called xe2x80x9cWB methodxe2x80x9d) is also used.
As the pattern tape for a TAB method, a tape for TAB is generally used. A tape for TAB has a three-layer structure in which an adhesive layer and a releasable polyester film, etc. used as a protective film layer are laminated onto a flexible organic insulating film such as a polyimide film.
Usually since the adhesive layer is arranged to be more narrow than the organic insulating film, the tape for TAB is generally produced by once producing an adhesive sheet and laminating it onto the organic insulating film.
The tape for TAB thus obtained undergoes (1) perforation to form sprocket and device holes, (2) thermal lamination with a copper foil and heating for curing the adhesive, (3) back treatment of the copper foil for forming inner leads, (4) pattern forming (resist coating, etching, resist removal, removal of copper foil back treating agent), (5) tin or gold plating, etc., to be processed into a connecting substrate (pattern tape). FIG. 3 shows the form of a pattern tape. FIG. 1 is a sectional view showing an embodiment of the TCP type semiconductor device of the present invention. The inner leads 5 of a pattern tape are thermally pressure-bonded to the gold bumps 2 of IC 1 (inner lead bonding), to mount the IC. Then, a sealing resin 10 is applied for sealing, to prepare a semiconductor device. In the case of TAB-BGA, the tape further undergoes a step of laminating a layer functioning as a reinforcing sheet, radiation sheet or shielding sheet, etc. using an adhesive sheet, and a step of installing solder balls.
For the WB method, a tape for WB suitable for wire bonding connection in adhesive properties is used, though the tape form and the production method are the same as those of the tape for TAB.
A tape for WB undergoes (1) perforation of sprocket and device holes, (2) thermal lamination with a copper foil and heating for curing the adhesive, (3) pattern forming (resist coating, etching, resist removal), (4) tin or gold plating, etc., to be processed into a connecting substrate (pattern tape) (FIG. 5). The pattern tape does not have inner leads, and the conductors of the pattern tape and the gold bumps of a semiconductor integrated circuit are wire-bonded to each other. Finally, as in the case of TAB method, a sealing resin is applied for sealing, to obtain a semiconductor device (FIG. 6).
The above TCP type semiconductor device is connected with a circuit board, etc. on which other parts are mounted, through outer leads or solder balls 9, to be mounted on an electronic apparatus.
The adhesive sheet for a semiconductor connecting substrate is required to have the following properties:
(a) High adhesive strength not allowing peeling even at a reflow temperature of 230xc2x0 C. or higher.
(b) Moderate elastic modulus and moderate coefficient of linear expansion to ease the thermal stress acting on the different materials forming the connecting substrate due to temperature cycles and reflow.
(c) Processability to allow sticking together and low temperature short time thermal cure.
(d) Insulatability in lamination on wiring.
Of the above properties, it has been especially difficult to achieve a balance between adhesive strength on the one hand and moderate elastic modulus and coefficient of linear expansion on the other hand. In the conventional adhesive compositions, if the adhesive strength is attempted to be improved, the elastic modulus at high temperature drops to pose a problem that totally satisfactory properties cannot be obtained.
In general, the adhesive strength of an adhesive can be enhanced by lowering the elastic modulus to increase the breaking energy, but this method presents a problem in that at high temperature and high humidity, the adhesive is softened, to lower the reflow resistance as well as the adhesive strength at high temperature and high humidity. On the other hand, if the crosslinking degree of the adhesive is increased to improve the reflow resistance and the adhesive strength at high temperature and high humidity, the adhesive is likely to cause brittle fracture, and the internal stress due to curing shrinkage increases, to unpreferably lower the adhesive strength on the contrary. Furthermore, the effect for easing the thermal stress caused by temperature difference is also lost.
An object of the present invention is to solve these problems, and to provide a new adhesive sheet for a semiconductor connecting substrate excellent in processability, adhesive strength, insulation reliability and durability, and also to provide a semiconductor connecting substrate and a semiconductor device using it.
On the other hand, the above mentioned tape for TAB has the following problems.
In the case of a TCP using a tape for TAB, since the adhesive layer of the tape for TAB finally remains in the package, it is required to satisfy such properties as insulatability, adhesiveness and dimensional stability. Since electronic apparatuses become smaller in size and higher in packaging density, the pattern pitches (conductor widths and conductor intervals) of semiconductor connecting substrates become very narrow, and so the adhesive is required to be higher in insulation reliability and in the adhesive strength to the copper foil more narrow in conductor width (hereinafter simply called xe2x80x9cadhesive strengthxe2x80x9d). Especially in an acceleration test of insulation reliability, the declining rate of insulation resistance at high temperature and high humidity of 130xc2x0 C. and 85% RH or with a voltage applied continuously in a high temperature range of 125xc2x0 C. to 150xc2x0 C. is now regarded to be highly important
However, in the above mentioned insulation reliability and adhesive strength, the conventional tapes for TAB are not satisfactory enough. For example, since the insulation drops fast when a voltage is applied continuously at high temperature and high humidity, the insulation reliability is insufficient. Especially when the calorific value is large in an integrated circuit acting at a high speed, etc., a serious accident can happen. Furthermore, since the adhesive strength is low, it can happen that conductors peel during pattern processing or that the inner leads peculiar to the TAB method are peeled, not allowing production.
Another object of the present invention is to solve these problems, and to provide a new tape for TAB excellent in insulation durability and adhesive strength, and a semiconductor connecting substrate and a semiconductor device using it.
Furthermore, the said tape for WB presents the following problems.
In the case of a TCP using a tape for WB, like the tape for TAB, since the adhesive layer remains in the package, high insulation reliability (at a high temperature and high humidity of 130xc2x0 C. and 85% RH) and adhesive strength at narrow pitches are also required. Furthermore, in the WB method, it can happen that the heating and ultrasonic wave application at the time of wire bonding soften the adhesive layer, not allowing wire bonding. So, heat resistance at the time of wire bonding (hereinafter called xe2x80x9cWBxe2x80x9d) is required.
However, in the above mentioned insulation reliability, adhesive strength and WB property, the conventional tapes for WB cannot be said to be satisfactory enough. For example, if the adhesive strength to the conductor is enhanced, the insulation with a voltage applied continuously at high temperature and high humidity drops fast, to show insufficient insulation reliability, and the WB property also drops. On the other hand, if the heat resistance is enhanced to improve the insulation reliability and WB property, the adhesive strength drops, causing the conductor to peel during pattern processing and also after completion of WB.
A further other object of the present invention is to solve these problems, and to provide a new tape for WB satisfying all of insulation durability, adhesive strength and WB property, and a semiconductor connecting substrate and a semiconductor device using it.
The above objects can be achieved by the following present invention. The present invention provides the following:
An adhesive sheet for a semiconductor connecting substrate being constituted by a laminate having an adhesive layer on a substrate, comprising said adhesive layer containing a thermoplastic resin (A) and an epoxy resin (B), and said epoxy resin (B) containing at least one epoxy resin (B) selected from (I) dicyclopentadiene skeleton-containing epoxy resins, (II) terpene skeleton-containing epoxy resins, (III) biphenyl skeleton-containing epoxy reins and (IV) naphthalene skeleton-containing epoxy resins, and a semiconductor connecting substrate and a semiconductor device using it.
Furthermore, an adhesive sheet for a semiconductor connecting substrate, which forms an adhesive layer (E) of a semiconductor integrated circuit board having at least one wiring board layer (C) being constituted by an insulator layer and a conductor pattern, at least one layer without any conductor pattern formed (D) and at least one adhesive layer (e), comprising said adhesive sheet has a storage elastic modulus of 0.1 to 10000 MPa and has a coefficient of linear expansion of 0.1xc3x9710xe2x88x925xcx9c50xc3x9710xe2x88x925xc2x0 C.xe2x88x921 in a temperature range of xe2x88x9250 to 150xc2x0 C. after having been cured by heating, and a semiconductor connecting substrate and a semiconductor device using it.
Still furthermore, an adhesive-backed tape for TAB being constituted by a laminate having an adhesive layer and a protective film layer on a flexible organic insulating film, comprising said adhesive layer has a softening temperature of 60 to 110xc2x0 C. after having been cured, and has an insulation resistance dropping time of 50 hours or more after having been allowed to stand in an environment of 130xc2x0 C. and 85% RH with DC 100 V applied, and a semiconductor connecting substrate and a semiconductor device using it.
Still furthermore, an adhesive-backed tape for wire bonding being constituted by a laminate having an adhesive layer and a protective film layer on a flexible organic insulating film, comprising said adhesive layer has a softening temperature of 120 to 200xc2x0 C. after having been cured and has a insulation resistance dropping time of 50 hours or more after having been allowed to stand in an environment of 130xc2x0 C. and 85% RH with DC 100 V applied.